1. Field of the Invention
The subject matter disclosed generally relates hard disk drives.
2. Background Information
Hard disk drives contain a plurality of heads that are magnetically coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
Information is stored in radial tracks that extend across the surface of each disk. Each track is typically divided into a number of segments or sectors. The voice coil motor and actuator arm can move the heads to different tracks of the disks.
Each sector may have a servo field located adjacent to a data field. The servo field contains a plurality of servo bits A, B, C and D that are read and utilized in a servo routine to position the head relative to the track. By way of example, the servo routine may utilize the algorithm of ((A−B)−(C−D)) to create a position error signal (“PES”). The PES is used to create a drive signal for the voice coil motor to position the head on the track.
The servo bits can be written onto the disk by initially writing reference servo bits onto one disk surface with a servo writer. After the drive is assembled the reference servo bits are used to write servo bits on the other disk surfaces. Copying servo from one disk to other disks within a sealed drive may result in track mis-registration.